Two-section complex coupled distributed feedback semiconductor laser with enhanced wavelength tuning range

Abstract

A complex coupled (gain coupled or loss coupled) distributed feedback (DFB) semiconductor laser, having two sections axially distinct along a cavity length direction, and two excitation means for independent pumping of corresponding sections of the laser in a master and slave type of pumping control, is provided. An extended continuous wavelength tuning range of the laser is obtained by selectively activating a left Bragg mode or a right Bragg mode across the stop band of the laser as a dominant lasing mode by the master and slave type of current injection control into different sections of the laser to alternate gain coupling and loss coupling mechanisms of laser operation, and further tuning a wavelength around the activated Bragg mode. Methods of operating the laser, enhancing a tuning range, and fabricating thereof are provided.

What is claimed is: 
     
       1. A distributed feedback single mode complex coupled semiconductor laser device, comprising: a) a substrate;   b) an active region formed thereon;   c) a complex-coupled grating structure having corrugations along a cavity length direction;   d) a first and a second excitation means for an independent pumping first and second sections of the laser axially distinct along a cavity length direction;   the laser device being characterized by means for varying the pumping of the first section of the laser with respect to the pumping of the second section of the laser in a master and slave type of pumping control for controllably activating a left Bragg mode or a right Bragg mode across the laser stop band by alternating use of anti-phase loss coupling or in-phase gain coupling mechanisms of laser operation.   
     
     
       2. A laser device of claim 1, further comprising means for tuning the laser wavelength around the left Bragg mode and the right Bragg mode correspondingly. 
     
     
       3. A laser device of claim 1, wherein the left Bragg mode is activated and the loss coupling mechanism of laser operation is provided by pumping the first section of the laser above a threshold level, the second section of the laser being unpumped or pumped in reverse or below a transparency level. 
     
     
       4. A laser device of claim 1, wherein the right Bragg mode is activated and the gain-coupling mechanism of laser operation is performed by pumping the first section of the laser above a transparency level and the second section above a threshold level. 
     
     
       5. A laser device of claim 1, wherein the active region comprises a multiple quantum well structure. 
     
     
       6. A laser device of claim 1, wherein the excitation means comprises an external optical pumping source. 
     
     
       7. A laser device of claim 1, wherein the excitation means comprises electrical contacts for current injection into the active region. 
     
     
       8. A laser device of claim 1, wherein a current confining region is formed on the active region. 
     
     
       9. A laser device of claim 8, wherein the excitation means comprises a first and a second electrodes formed on a top of the current confining region. 
     
     
       10. A laser device of claim 8, wherein the current confining region is a ridge waveguide. 
     
     
       11. A laser device of claim 8, wherein the current confining region is a buried heterostructure-structure. 
     
     
       12. A laser device of claim 1, wherein the grating structure is a chirped grating or a uniform grating. 
     
     
       13. A laser device of claim 1, wherein the grating structure comprises periodic etched grooves through the active region. 
     
     
       14. A laser device of claim 1, wherein the grating structure comprises a first grating section and a second grating section positionally corresponding to the first and the second sections of the laser. 
     
     
       15. A laser device of claim 14, wherein the first and the second grating sections have the same corrugation period. 
     
     
       16. A laser device of claim 14, wherein the first and the second grating sections have different corrugation periods. 
     
     
       17. A laser devices of claim 14, wherein the corrugation periods of the first and the second grating sections differ so that to provide a center Bragg wavelength separation of the grating sections within a range of several nanometers to several tens of nanometers. 
     
     
       18. A distributed feedback single mode complex coupled semiconductor laser device, comprising: a) a substrate;   b) a bottom electrode formed on a bottom surface of the substrate;   c) an active region formed on the substrate, comprising a multiple quantum well structure;   d) a complex coupling grating formed by periodic etching grooves through the active region along a cavity length direction;   e) a current confining ridge on the active region, and   f) a first electrode and a second electrode, formed on a top of the current confining ridge for independent current injection into a first section and a second section of the laser axially distinct along a cavity length direction,   the laser device being characterized by means for varying the current injection through the first electrode with respect to the current injection through the second electrode in a master and slave type of current injection control for controllably activating a left Bragg mode or right Bragg mode across the laser stop band by alternating use of anti-phase loss coupling or in-phase gain coupling mechanisms of laser operation, and tuning the lasing wavelength around the left Bragg mode and the right Bragg mode by varying the correspondent current injection.   
     
     
       19. A laser device of claim 18, wherein the left Bragg mode is activated by biasing the first section of the laser above a threshold level, the second section of the laser being unbiased, biased in reverse or below a transparency level, the loss coupling mechanism of laser operation being provided. 
     
     
       20. A laser device of claim 18, wherein the right Bragg mode is activated by biasing the first section of the laser above a transparency level and the second section above a threshold level, the gain coupling mechanism of laser operation being provided. 
     
     
       21. A laser device of claim 18, wherein a depth of the grooves of the grating structure is equal to a thickness of the active region. 
     
     
       22. A laser device of claim 18, wherein a depth of the grooves of the grating structure is less than a thickness of the active region. 
     
     
       23. A laser device of claim 18, wherein the grating is a first order grating. 
     
     
       24. A laser device of claim 18, wherein the grating is a chirped grating. 
     
     
       25. A laser device of claim 18, wherein a side-mode suppression ratio of the Bragg modes over 45 dB is achieved. 
     
     
       26. A laser device of claim 18, wherein the substrate is of N-type and the current confining ridge is of P-type. 
     
     
       27. A laser device of claim 18, wherein the substrate is of P-type and the current confining ridge is of N-type. 
     
     
       28. A laser device of claim 18, wherein the substrate is made of InP. 
     
     
       29. A laser device of claim 28, wherein a wavelength of generated light is within a range of 1.3-1.56 μm. 
     
     
       30. A laser device of claim 18, wherein the substrate is made of GaAs. 
     
     
       31. A laser device of claim 30, wherein a wavelength of generated light is within a range of 0.8-0.9 μm. 
     
     
       32. A method of operating a distributed feedback complex coupled semiconductor laser device, having a first section and a second section of the laser axially distinct along a cavity length direction, and a first excitation means and a second excitation means for an independent pumping of the corresponding section of the laser, the method comprising: varying the pumping of the first section of the laser with respect to the pumping of the second section of the laser in a master and slave type of pumping control for controllably activating a left Bragg mode or a right Bragg mode across the laser stop band by alternating use of anti-phase loss coupling or in-phase gain coupling mechanisms of laser operation.   
     
     
       33. A method of claim 32, comprising an additional step of tuning the laser wavelength around the left and the right Bragg modes correspondingly. 
     
     
       34. A method of claim 32, wherein the step of varying the pumping in the master and slave type of pumping control comprises pumping the first section of the laser above a threshold level, the second section of the laser being unpumped or pumped below a transparency level, the left Bragg mode being activated and the loss coupling mechanism of laser operation being provided. 
     
     
       35. A method of claim 32, wherein the step of varying the pumping in the master and slave type of pumping control comprises pumping the first section of the laser above a transparency level and the second section above a threshold level, the right Bragg mode being activated and the gain coupling mechanism of laser operation being provided. 
     
     
       36. A method of claim 32, wherein the step of varying the pumping comprises fast wavelength switching between the left Bragg mode and the right Bragg mode within a time interval of several nanoseconds. 
     
     
       37. A method of claim 32, wherein the step of varying the pumping comprises periodic fast wavelength switching between the left Bragg mode and the right Bragg mode within a time interval of several nanoseconds, the method further comprising the steps of: periodic modulation of the left Bragg mode and the right Bragg mode when the corresponding mode is activated;   separation of left and right Bragg modes by optical filtering techniques.   
     
     
       38. A method of enhancing a tuning range in a distributed feedback complex coupled semiconductor laser device, having a first section and a second section of the laser axially distinct along a cavity length direction, and a first electrode and a second electrode for an independent current injection into the corresponding section of the laser, the method comprising: varying the current injection through the first electrode with respect to the current injection through the second electrode in a master and slave type of current injection control for controllably activating a left Bragg mode or a right Bragg mode across the laser stop band by alternating use of anti-phase loss coupling or in-phase gain coupling mechanisms of laser operation; and   tuning the laser wavelength around the left and the right Bragg modes by varying the corresponding current injection.   
     
     
       39. A method of claim 38, wherein the step of varying the current injection in a master and slave type of injection control comprises biasing the first section of the laser above a threshold level, the second section of the laser being unbiased, biased in reverse or below a transparency level, the left Bragg mode being activated and the loss coupling mechanism of laser operation being provided. 
     
     
       40. A method of claim 38, wherein the step of varying the current injection in a master and slave type of injection control comprises biasing the first section of the laser above a transparency level and the second section above a threshold level, the right Bragg mode being activated and the gain coupling mechanism of laser operation being provided. 
     
     
       41. A method of fabricating a distributed feedback single mode complex coupled semiconductor laser device, comprising: a) providing a substrate;   b) forming an active region thereon;   c) forming a complex coupled grating structure having corrugations along a cavity length direction;   d) providing a first excitation means and a second excitation means for an independent pumping of a first section and a second section of the laser axially distinct along a cavity length direction;   e) providing means for varying pumping of the first section of the laser with respect to the pumping of the second section of the laser in a master and slave type of control for controllably activating a left Bragg mode or a right Bragg mode across the laser stop band by alternating use of anti-phase loss coupling or in-phase gain coupling mechanisms of laser operation;   f) providing means for tuning the laser wavelength around the left and the right Bragg modes correspondingly.   
     
     
       42. A method of fabricating a distributed feedback single mode complex coupled semiconductor laser device, comprising: a) providing a semiconductor substrate;   b) forming a bottom electrode on a bottom surface of the substrate;   c) forming an active region on the substrate comprising a multiple quantum well structure;   d) forming a complex coupled grating formed by periodic etching grooves through said active region along a cavity length direction;   e) forming a current confining ridge on the active region;   f) forming a first electrode and a second electrode on a top of the current confining ridge for an independent current injection into a first section and a second section of the laser axially distinct along a cavity length direction;   g) providing means for varying the current injection through the first electrode with respect to the current injection through the second electrode in a master and slave type of current injection control for controllably activating a left Bragg mode or a right Bragg mode across the laser stop band by alternating use of anti-phase loss coupling or in-phase gain coupling mechanisms of laser operation;   h) providing means for tuning the laser wavelength around the left Bragg mode and the right Bragg mode correspondingly.